1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method of allocating essential control information in a frame supporting heterogeneous systems.
2. Related Art
The institute of electrical and electronics engineers (IEEE) 802.16 standard provides a technique and protocol for supporting broadband wireless access. The standardization had been conducted since 1999 until the IEEE 802.16-2001 was approved in 2001. The IEEE 802.16-2001 is based on a physical layer of a single carrier (SC) called ‘WirelessMAN-SC’. The IEEE 802.16a standard was approved in 2003. In the IEEE 802.16a standard, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ are further added to the physical layer in addition to the ‘WirelessMAN-SC’. After completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors of the IEEE 802.16-2004 standard, the IEEE 802.16-2004/Cor1 (hereinafter, IEEE 802.16e) was completed in 2005 in a format of ‘corrigendum’.
Communication between a base station (BS) and a user equipment (UE) includes downlink (DL) transmission from the BS to the UE and uplink (UL) transmission from the UE to the BS. A system profile based on the existing IEEE 802.16e supports a time division duplex (TDD) scheme in which DL transmission and UL transmission are divided in a time domain. In the TDD scheme, UL transmission and DL transmission are performed at different times by using the same frequency band. The TDD scheme has an advantage in that frequency selective scheduling is simply performed since a UL channel characteristic and a DL channel characteristic are reciprocal.
At present, there is ongoing standardization effort for the IEEE 802.16m standard which is a new technical standard based on the IEEE 802.16e. The IEEE 802.16e system considers not only a frequency division duplex (FDD) scheme but also a half-duplex FDD (H-FDD) scheme. In the FDD scheme, DL transmission and UL transmission are simultaneously performed by using different frequency bands. In the H-FDD scheme, DL transmission and UL transmission are performed at different times by using different frequency bands. That is, the H-FDD scheme does not perform DL transmission and UL transmission simultaneously, and a DL radio resource and a UL radio resource are not allocated to a UE using the H-FDD scheme in the same time domain.
An evolution system evolved from a legacy system has to be designed to operate by incorporating the legacy system, which is referred to as backward compatibility. To satisfy the backward compatibility, the evolution system has to be able to support not only the TDD scheme but also the FDD scheme, the H-FDD scheme, etc. As various transmission schemes are supported, essential control information needs to be provided for each of the legacy system and the evolution system. The essential control information is control information that must be acquired by all UEs using the system. Examples of the essential control information include system information to be broadcast, synchronization information, etc. The essential control information for the evolution system is preferably provided without having an effect on the essential control information of the legacy system.
However, how to allocate the essential control information in the evolution system satisfying backward compatibility with the legacy system is not provided yet.